We wish to delineate ontogenetically and phylogenetically the inductor and effector limbs of the immune response. Two principal areas will be investigated: 1) the development of immunocytes after recognition, binding, and reaction to antigen; and 2) the maturation of immuno-competence. Antigen recognition is crucial to the inductive phase of the immune response. Final sequestration of antigen involves the effector phase. Antigen recognition and the events that follow will be assessed by several parameters: enumeration of antigen binding cells, quantitation of stimulated cells, and the measurement of cell mediated or humoral immunity. When viewed from the ontogenetic and phylogenetic perspective, this proposal will elucidate where recognition, binding and reaction to antigen first appear. The results will be viewed as necessary biologic data for understanding how the human immune system developed and what may occur as it undergoes senescence.